Sampling method and apparatus

ABSTRACT

A method of sampling comprises regulating the flow of a carrier liquid at two points between which is located the sample source, the rate of flow upstream of the source being arranged to be less than that downstream of the source, the difference in rate being made up by withdrawal of a sample into the carrier liquid.

United States Patent Broadbent et a]. 1 Oct. 3, 1972 [54] SAMPLING METHOD AND [56] References Cited APPARATUS UNITED STATES PATENTS [72] Inventors: Graham Broadbent; John Rickard M fi ld both f Stocktomon- 3,444,722 5/1969 Roof ..73/23.l Tees, E l d 3,038,340 6/ I962 lsreeli ..73/423 A [73 Assignee: b0 ghemcall' dIndustries Primary Examiner bouis Prince n ng Assistant ExaminerWilliam A. Henry, II [22] Filed: March 30, 1970 Attorney-Cushman, Darby & Cushman [21] Appl. No.: 23,725 I ABSTRACT A method of sampling comprises regulating the flow [30] Forelgn Apphcamm i i Data of a carrier liquid at two points between which is M91611 1969 Great Brlialn located the sample source, the rate of flow upstream of the source being arranged to be less than that U.S. downstrea n of the ource the difierence in rate being Int. Cl. "G011! made up withdrawal of a sample into the carrier [58] Field of Search.73/42l R, 423 A, 421 B, 422 R,

liquid.

11 Claims, 3 Drawing Figures mimsuncrs lav 3.695.113

SAMPLING METHOD AND APPARATUS The present invention relates to a method and apparatus for sampling a liquid.

According to the invention a method of sampling a liquid comprises regulating the flow of a carrier liquid at two points between which is located the source of the liquid to be sampled, the rate of flow at the point upstream of the source being regulated so as to be less than at the point downstream of the source, liquid from the source being drawn into the carrier to make up the difference in rate.

An apparatus for use in the method of the invention comprises two flow regulators located one at each end of two arms of a T-piece, the end of the third arm of the T-piece being attachable to a source of the liquid to be sampled. Means are also provided to connect the two flow regulators to a source of carrier liquid and a sample receptacle respectively.

Preferably the two flow regulators are disposed rectilinearly in series.

The invention is of particular use in collecting a sample for analytical purposes from a chemical reactor. If a reaction is being carried out in a continuous manner a sample may also be taken continuously at a constant rate and submitted, if desired, to a continuous automatic analyzer such as a vapor-phase chromatographic analyzer. In such an application the carrier liquid is generally inert and is chosen so that it does not interfere either with the liquid to be sampled or with any subsequent analytical procedure. The carrier liquid need not necessarily be inert however and in certain instances it may be desirable that some reaction should take place between the carrier and the liquid to be sam pled, and this can be arranged. From what has been said it will be clear that the carrier liquid can only be chosen by reference to the circumstances of each individual application. Water, however, is a common and easily obtained carrier liquid which is frequently suitable.

The rates of flow at the two flow regulators upstream and downstream of the sample source are arranged to supply the desired rate of liquid which is being sampled. For analytical purposes the rate of sample withdrawal is suitably 1 to 20 mls./minute the corresponding rate of carrier liquid flow being 9 to I80 mls./minute at a carrier liquid to sample ratio of 9:1. This ratio may however be varied and may for example lie in the range 2:l to 20:1. Preferred flow regulators are pumps pumping at different rates but other devices such as an injector and an ejector delivering and withdrawing measured amounts of liquid may also be used. Most types of pump may be used in the process but we have found diaphragm pumps to be particularly suitable. In a preferred arrangement the two flow regulators, e.g. diaphragm pumps, are adapted by suitable means such as a timer controlling the flow actuators to operate in a regularly intermittent manner out of phase with each other. Thus the upstream regulator supplies a quantity of carrier liquid when the downstream regulator is not operating so that the carrier liquid is forced up the third arm of the T-piece to flush out the liquid to be sampled. The upstream regulator then stops and the downstream regulator is brought into operation so that both carrier liquid and the sample are withdrawn. By operating in this manner regular pulses of carrier liquid and sample are obtained the relative amounts of carrier liquid and sample in each pulse and the quantity, of the pulse being constant. When operating in this manner it is preferable to maintain the connecting lines between the flow regulators and the sample source as short as possible to keep the time constant of the device to a minimum.

The pressure at which the carrier liquid is supplied by the upstream flow regulator is greater than the pressure at which the liquid which is to be sample is maintained. Suitably the pressure difference is p.s.i.

The source of the liquid to be sampled, the sampling device, and, if desired, an analytical apparatus form a sealed system, so corrosive, toxic or unstable liquids can readily be sampled. When the liquid to be sampled contains a dissolved gas a novel let-down vessel may advantageously be interposed between the source of liquid to be sampled and the sampling device. Suitably the let-down vessel may, be cylindrical in shape the liquid being capable of introduction, preferably tangentially, so as to run down the walls in a thin film to a withdrawal point at the bottom of the vessel. The gas which is released from the film to the center of the vessel is suitably removed. This device is very useful in sampling an oxidation reaction in which, in the absence of oxygen, catalyst precipitates because the falling film although releasing oxygen is still maintained in contact with an oxygen atmosphere. An example of such a reaction is the liquid phase oxidation of an olefine, e.g. ethylene, to an unsaturated ester, e.g. vinyl acetate, in the presence of a soluble palladous salt and cupric salt catalyst and molecular oxygen. In the absence of oxygen the palladous salt is reduced to metallic palladium which precipitates and the cupric salt is reduced to the cuprous form. By use of the present invention a sample of liquor containing the palladous and cupric salts may be removed, degassed and analyzed without substantial formation of the cuprous state and precipitation of palladium. The sampling device constructed in accordance with the present invention may also be used to sample slurries particularly by means of the preferred embodiment described above in which intermittent operation is used and the third arm of the T- piece is flushed out with the carrier liquid.

The invention will now be further described with reference to the following drawings in which:

FIG. 1: is a longitudinal section of a let down vessel.

FIG. 2: is a transverse section of the let down vessel, showing the tangential location of the sample inlet.

FIG. '3: is a plan of the sampling device.

The let down vessel comprises a cylinder 1 provided with a sample inlet port 2 located so as to inject the sample in a direction tangential to the internal wall of the cylinder. The cylinder is also fitted with a gas exit port 3 and liquid exit ports 4 and 5 respectively. The liquid exit port 4 is surrounded by a weir 6 while exit port 5 is adapted to supply the sample to the sampling device.

In operation the liquid sample is injected tangentially via inlet port 2 so that it falls in a thin continuous film down the inner surface of the cylinder 1. At the point of entry 2 there is a pressure drop so that gas contained in the liquid sample is released and escapes through the gas exit port 3. Control of pressure at this port controls the pressure in the system. When the liquid reaches the base of the cylinder it runs into the exit port 5 and thence to the sampling device. Excess liquid sample may be withdrawn via the exit port 4 over the weir 6.

The sampling device comprises two diaphragm pumps 7 and 8 and associated valves 16 and 17 connected in series by a pipe 9 provided with a branch 10 intermediate between the two pumps. The diaphragms 1 l and 12 of the two pumps are connected to actuators l3 and 14 respectively which in turn are linked to a timer 15. Pump 7 is adapted to be connected to a source of carrier liquid and pump 8 as adapted to deliver the carrier liquid and sample.

The diaphragms 11 and 12 of the two pumps are driven by pulses from the actuators l3 and 14 the timer being used to ensure that the pulses are 180 out of phase and that the stroke time is less than the interval between pulses. Pump 8 is set to dispense a preset greater quantity of liquid than pump 7, the difference representing the size of the sample. Operation of the diaphragm ll draws in carrier liquid to pump 7 and then delivers it as a pulse to pipe 9. The pulse passes along pipe 9 and into branch 10 which is connected to the source of sample. The diaphragm 12 of pump 8 then operates to draw the carrier liquid and sample into the pump and finally to dispense this liquid to, for example, an analytical apparatus.

We claim:

1. A method of sampling a liquid which comprises providing a flow of a carrier liquid between an upstream point and a downstream point, locating a source of the liquid to be sampled between said points, connecting said source to said flow and regulating the flow of said carrier liquid at said two points, the rate of flow of said carrier liquid upstream of the source being regulated so as to be less than at the point downstream of the source whereby liquid from the source is drawn into said carrier liquid to make up the difference in rate.

2. The method of claim 1 in which the carrier liquid is water.

3. The method of claim 1 in which said liquid to be sampled is a liquor containing palladous and cupric salts from a liquid-phase olefine oxidation process.

4. The method of claim 1 in which the ratio of the rate of flow of carrier liquid to the rate of sample withdrawal is in the range 2:1 to 20:1.

5. The method of claim 4 in which said ratio is 9:l and the rate of sample withdrawal 1 to 20 mls/minute and the rate of carrier liquid flow 9 to mls/minute.

6. The method of claim 1 in which said carrier liquid is supplied at a pressure 50 psi. greater than the pressure of the liquid to be sampled.

7. An apparatus for use in sampling a liquid by regulating the flow of a carrier liquid at two points between which is located the sample source, the rate of flow upstream of the source being arranged to be less than that downstream of the source, the difference in rate being made up by withdrawal of a sample into the carrier liquid, said apparatus comprising a T-piece, two flow regulators located one at each end of two arms of said T-piece, and means to connect the third arm of said T- piece to a source of the liquid to be sampled.

8. The apparatus of claim 7 in which said flow regulators are pumps.

9. The apparatus of claim 7 in which a timer is provided, connpcted to said flow regulators to control the operation 0 said regulators in a regu arly intermittent manner out of phase with each other.

10. The apparatus of claim 7 in which a let-down vessel is provided, located between and connected to the source of said liquid to be sampled and said sampling apparatus.

1 l. The apparatus of claim 10 in which said let-down vessel is cylindrical in shape provided with sample inlet and gas exit at the top of the cylinder and sample withdrawal at the bottom of the cylinder, liquid to be sampled being capable of introduction into the letdown vessel through the inlet so as to run down the walls of the vessel as a thin film to said sample withdrawal at the bottom of the cylinder, gas released from the liquid sample leaving said vessel by the gas exit. 

1. A method of sampling a liquid which comprises providing a flow of a carrier liquid between an upstream point and a downstream point, locating a source of the liquid to be sampled between said points, connecting said source to said flow and regulating the flow of said carrier liquid at said two points, the rate of flow of said carrier liquid upstream of the source being regulated so as to be less than at the point downstream of the source whereby liquid from the source is drawn into said carrier liquid to make up the difference in rate.
 2. The method of claim 1 in which the carrier liquid is water.
 3. The method of claim 1 in which said liquid to be sampled is a liquor containing palladous and cupric salts from a liquid-phase olefine oxidation process.
 4. The method of claim 1 in which the ratio of the rate of flow of carrier liquid to the rate of sample withdrawal is in the range 2:1 to 20:1.
 5. The method of claim 4 in which said ratio is 9:1 and the rate of sample withdrawal 1 to 20 mls/minute and the rate of carrier liquid flow 9 to 180 mls/minute.
 6. The method of claim 1 in which said carrier liquid is supplied at a pressure 50 p.s.i. greater than the pressure of the liquid to be sampled.
 7. An apparatus for use in sampling a liquid by regulating the flow of a carrier liquid at two points between which is located the sample source, the rate of flow upstream of the source being arranged to be less than that downstream of the source, the difference in rate being made up by withdrawal of a sample into the carrier liquid, said apparatus comprising a T-piece, two flow regulators located one at each end of two arms of said T-piece, and means to connect the third arm of said T-piece to a source of the liquid to be sampled.
 8. The apparatus of claim 7 in which said flow regulators are pumps.
 9. The apparatus of claim 7 in which a timer is provided, connected to said flow regulators to control the operation of said regulators in a regularly intermittent manner out of phase with each other.
 10. The apparatus of claim 7 in which a let-down vessel is provided, located between and connected to the source of said liquid to be sampled and said sampling apparatus.
 11. The apparatus of claim 10 in which said let-down vessel is cylindrical in shape provided with sample inlet and gas exit at the top of the cylinder and sample withdrawal at the bottom of the cylinder, liquid to be sampled being capable of introduction into the let-down vessel through the inlet so as to run down the walls of the vessel as a thin film to said sample withdrawal at the bottom of the cylinder, gas released from the liquid sample leaving said vessel by the gas exit. 